In Beer's law, if path length doubles and concentration stays the same, what happens to absorbance?

In Beer's law, if path length doubles and concentration stays the same, what happens to absorbance?

• A. Absorbance doubles.
• B. Absorbance halves.
• C. Absorbance remains the same.
• D. Absorbance quadruples.

Answer: (A)

Absorbance depends directly on how far light travels through the sample and how many absorbing molecules are present, described by A = ε l c. If the path length doubles while the concentration stays the same, the absorbance doubles as well: A' = ε (2l) c = 2A. The molar absorptivity ε remains constant for a given wavelength, so nothing offsets the change. This linear relationship holds within Beer's law’s valid range; deviations can occur at very high absorbances, but the direct proportionality to path length explains why absorbance doubles here.

Absorbance depends directly on how far light travels through the sample and how many absorbing molecules are present, described by A = ε l c. If the path length doubles while the concentration stays the same, the absorbance doubles as well: A' = ε (2l) c = 2A. The molar absorptivity ε remains constant for a given wavelength, so nothing offsets the change. This linear relationship holds within Beer's law’s valid range; deviations can occur at very high absorbances, but the direct proportionality to path length explains why absorbance doubles here.